A typical data storage system includes one or more data storage disks coaxially mounted on the hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute. Digital information is typically written to and read from the data storage disks by one or more magnetic transducers, or read/write heads, which are mounted to an actuator and moved radially above and/or below the surfaces of the rotating data storage disks.
The actuator typically includes a plurality of outwardly extending actuator arms, with one or more magnetic read/write transducers being mounted resiliently or rigidly on the extreme end of the actuator arms. The actuator arms are interleaved into and out of the stack of rotating magnetic disks, typically by means of a coil assembly mounted to the actuator. The coil assembly generally interacts with a permanent magnet structure, and the application of current to the coil in one polarity causes the actuator arms and transducers to shift in one direction, while current of the opposite polarity shifts the actuator arms and transducers in an opposite direction.
In a typical digital data storage system, digital information is stored in the form of magnetic energization on a series of concentric, closely spaced tracks arranged on the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a plurality of sectors. One of the informational fields is typically designated for storing data, while other fields contain sector identification and synchronization information, for example. Data is transferred to, and retrieved from, specified track and sector locations by the magnetic transducers being shifted from track to track, typically under the control of a controller provided in the data storage system. The transducer assembly typically includes a read element and a write element.
Writing data to a data storage disk generally involves passing a current through the write element of the transducer assembly to produce magnetic lines of flux which magnetize a specific location of the disk surface. Reading data from a specified disk location is typically accomplished by a read element of the transducer assembly sensing the magnetic field or flux lines emanating from the magnetized locations of the disk. As the read element moves over the rotating disk surface, the interaction between the read element and the magnetized locations on the disk surface result in voltage pulses being induced in the read element. The voltage pulses represent transitions in the magnetic field and demarcate the data storing locations of the disk.
Conventional data storage systems generally employ a closed-loop servo control system for accurately and rapidly positioning the actuator and read/write transducers to specified storage locations on the data storage disk. A servo writing procedure is typically implemented to record servo information on the surface of one or more data storage disks comprising the data storage system. A servo writer assembly is typically used by manufacturers of data storage systems to facilitate the transfer of servo data to one or more data storage disks during the manufacturing process. In accordance with a known servo information format, termed an embedded servo, servo information is written between the data storing sectors of each track. The servo data is thus embedded in the data storing tracks of the data storage disks, typically resulting in an alternating sequence of data and servo sectors comprising each track. In accordance with another known servo information format employed in data storage systems, termed a dedicated servo, the servo writer records servo information typically on only one of the data storage disks comprising the disk stack, and often on only one of surfaces of the dedicated servo disk. The servo information stored on the dedicated servo disk is used to maintain accurate positioning and alignment of the read/write transducers associated with each of the data storage disks. During normal data storage system operation, a servo transducer, generally mounted proximate the read/write transducers, is typically employed to read the servo sector data for the purpose of locating specified track and data sector locations on the disk. It is noted that a servo sector typically contains a pattern of data bits, often termed a servo burst pattern, used to maintain optimum alignment of the read/write transducers over the centerline of a track when reading and writing data to specified data sectors on the track.
In high capacity data storage systems, it is generally desirable to employ data storage disks having track densities in excess of three thousand tracks per radial inch. In an effort to maximize the amount of disk surface area available for storing data, the width of each track and the distance separating adjacent tracks is generally reduced to a minimal dimension, with the minimum track width and separation distance between adjacent tracks being dictated by the physical dimensions of the read/write and servo transducers. Track occlusion, generally associated with the overlapping or obscuring of track boundaries, also impacts the minimum track width and separation distance between adjacent tracks. To ensure accurate track seeking and alignment when reading and writing data to the disk, the servo writer must precisely and reliably record the servo data on the disk during the servo writing procedure, which is typically performed at the data storage system manufacturing facility.
A conventional method and apparatus for writing servo information to a data storage disk is illustrated in FIG. 2. An actuator 30, with one or more transducers 27 mounted to the end of the actuator arms 28, is engaged by a separate linear displacement assembly 60 which produces a torquing force on the actuator 30 causing the actuator arms 28 and read/write transducers 27 to move radially across the data storage disk surfaces 24. It is noted that a servo writer assembly generally utilizes the read/write transducers 27 of the data storage system 20 to record servo information on the data storage disks 24 during the servo writing procedure, rather than utilizing a separate transducer and actuator assembly. The linear displacement assembly 60 typically includes a push-rod 62 which extends through a relatively large window 64 provided in a sidewall 29 or other portion of the housing base 22. The push-rod 62 is generally coupled to a coupling rod 61 extending outwardly from the back end 37 of the actuator 30. Alternatively, the actuator back end 37 may include a receiving hole 66 for receiving the push-rod 62. It is noted that the coil assembly 36 and coil frame 34 are omitted from the actuator 30 illustration of FIG. 2 for purposes of clarity.
The linear displacement assembly 60 displaces the push-rod 62 in a forward and reverse linear direction which, in turn, exerts a localized torquing force at the actuator 30/push-rod 62 interface 66 on the back end 37 of the actuator 30, thereby causing the actuator 30 to rotate. The linear displacement assembly 60 typically displaces the push-rod 62 with a relatively high degree of precision in an attempt to accurately locate the transducers 27 typically above the centerline of the tracks 50 while writing servo information to the servo sectors 52 on the data storage disk 24. The linear displacement assembly 60, push-rod 62, and actuator 30 must generally operate to precisely position the transducers 27 above the centerline of the tracks 50 to avoid unintended positional shifting of the transducers 27 and to avoid undesirable rotational movement of the transducers 27 into the narrow gap separating adjacent tracks 50 when writing servo data to the data sectors 52. It can be appreciated that any appreciable amount of unintended residual movement of the actuator 30 during the servo writing procedure can result in the misalignment of the transducers 27 when writing servo data to the disks 24 and subsequent read/write errors of varying severity.
A major source of transducer 27 misalignment occurring during the servo writing procedure has been determined to be associated with residual shifting or settling of a ball bearing assembly 70 employed to facilitate actuator 30 rotation. As illustrated in FIG. 3, a conventional bearing cartridge 70 includes a number of individual precision machined ball bearings 72 encased within a circular bearing cartridge 70. In practice, the inner diameter of the bearing cartridge 70 mechanically engages a stationary actuator shaft 32, while the outer diameter of the bearing cartridge 70 mechanically engages the inner diameter of a cylindrical bore 96 defining the rotational axis of the actuator 30. It has been determined that the traditional approach of moving the actuator 30 during the servo writing procedure with a conventional linear displacement assembly 60 and push-rod 62, as illustrated in FIG. 2, produces a torquing force localized at the actuator 30/push-rod 62 interface 66 which is imparted to the bearing cartridge 70 as a torquing force 74 localized at a single contact region 75 on the bearing cartridge 70. This localized torquing force 74 impinging on the bearing cartridge 70 contact region 75 results in unintended residual movement or settling of the ball bearings 72 within the bearing cartridge 70 after the actuator 30 has been precisely positioned at a specified servo sector location. The undesirable residual shifting of the bearings 72 and bearing cartridge 70 results in a corresponding positional shifting of the actuator 30 and transducers 27 while servo information is being written to the data storage disks 24. As track 50 densities continue to increase, the residual shifting of the ball bearings 72 and bearing cartridge 70 has become a major contributor to incidents of transducer 27 misalignment and servo information recording errors arising during the servo writing procedure.
Another source of servo writing errors associated with a conventional linear displacement assembly 60 concerns the relationship between the movement of the push-rod 62 and the resulting rotation of the actuator 30. More particularly, as the actuator 30/push-rod 62 interface 66 rotates away from a perpendicular orientation with respect to the linear displacement assembly 60, the magnitude of push-rod 62 displacement is non-linearly related to the magnitude of the resulting actuator 30 rotation. Those skilled in the art can appreciate the difficulty of controlling the non-linear cooperative movement between the linear displacement assembly 60 and rotatably mounted actuator 30 to effectuate high-precision positioning of the transducers 27 during the servo writing procedure.
A trend has developed in the data storage system manufacturing community to miniaturize the chassis or housing of a data storage system to a size amenable for incorporation into miniature personal computers, such as lap-top computers, for example. Various industry standards have emerged that specify the external housing dimensions of small and very small form factor data storage systems. One such recognized family of industry standards is the PCMCIA (Personal Computer Memory Card Industry Association) family of standards, which specifies both the dimensions for the data storage system housing and the protocol for communicating control and data signals between the data storage system and a host computer system coupled thereto. Recently, four families or types of PCMCIA device specifications have emerged. By way of example, a Type-I PCMCIA data storage system must be fully contained within a housing having a maximum height dimension of 3.3 millimeters (mm). By way of further example, a Type-II PCMCIA device housing must not exceed a maximum height of 5.0 mm in accordance with the PCMCIA specification. A maximum height of 10.5 mm is specified for the housing of Type-III PCMCIA devices, and Type-IV devices are characterized as having a maximum housing height dimension in excess of 10.5 mm.
The structural stability of the protective housing of small and very small form factor data storage systems is of particular concern as the thickness dimensions of the housing structure of such systems continue to be reduced in order to meet the stringent dimensional requirements specified by the PCMCIA and other industry standards, as well as to minimize the weight of data storage systems. The extremely compact housing configuration of small and very small form factor data storage systems require that the sensitive internal components be placed in close proximity to one another. Any appreciable distortion or warping of the housing base or cover can result in deleterious contact between adjacent components, often resulting in catastrophic damage to the data storage system. It has been determined that by providing an access window 64 having dimensions sufficient to accommodate the push-rod 62 of a conventional linear displacement assembly 60, the structural integrity of the data storage system housing for relatively small and very small form factor data storage systems may be adversely compromised. Moreover, it is believed that an access window 64 suitable for accommodating a conventional linear displacement assembly 60 and push-rod 62 would severely compromise the structural integrity of a non-metallic housing structure for relatively small form factor data storage systems.
There exists a need in the data storage system manufacturing industry for a servo writer apparatus and methodology that provides accurate and stable positioning of the actuator and transducer when writing servo information to a data storage disk. There exists the further need to provide a means for accessing the actuator through the housing of a data storage system by an external servo writer in a manner which does not adversely affect the structural integrity of the housing. The present invention fulfills these and other needs.